Method and apparatus for delivering secured telephony service in a hybrid coaxial cable network

ABSTRACT

A hybrid coaxial cable network employing interdiction to ensure privacy in telephony communications. The video and telephony signals are secured such that telephony and interactive video signals to and from a subscriber do not appear on the network at any other undesired subscriber location.

This is a continuation of application Ser. No. 08/467,343, filed Jun. 6,1995, now U.S. Pat. No. 5,559,858; which is a continuation ofapplication Ser. No. 08/357,558, filed Dec. 16, 1994, now U.S. Pat. No.5,469,495; which is a continuation of application Ser. No. 08/069,227,filed May 28, 1993, now abandoned.

FIELD OF THE INVENTION

The invention relates to the field of telecommunications. Moreparticularly the invention relates to the field of multiplexcommunications. In still greater particularity, the invention relates tothe provision of secured telephony in a coaxial cable network. By way offurther characterization, but not by way of limitation thereto, theinvention uses interdiction to prevent monitoring of a subscriber'stelephone communications by another subscriber on the network.

DESCRIPTION OF THE PRIOR ART

Information, and access to it, has received significant attentionrecently. The building of an “information highway” compared to thenational interstate highway system begun in the 1950s has been made anational priority. There are currently three wireline transport elementsavailable for such a highway: (1) fiber optic cable; (2) coaxial cable;and (3) twisted copper pair cable (“twisted pair”). Presently, twistedpair cable predominates, certainly in the local loop portion oftelephone networks. Coaxial cable has been used widely by cabletelevision companies. Both telephone companies and cable companies havemade use of fiber optics for main or trunk line signal transport.

Fiber optic cable can carry more information over a greater distancethan coaxial cable, while coaxial cable can carry more information overa greater distance than twisted pairs. Because twisted pair is thepredominant local loop technology, at least in the telephone industry,attempts have been made to develop technologies which will increase thecarrying capacity of copper. In reality, copper wire is a very efficienttransport means for traditional telephony services.

Within the telephony industry, the term “broadband” denotes a very highdigital line rate, such as the 156 Megabits per second (Mb/s) opticalline rate of new SONET OC3-level fiber optic systems The term “baseband”describes the original (unmodulated) form of the electrical or opticalsignal associated with a single service that is typically presented tothe network by a subscriber, and the final form of that signal presentedfrom the network to a subscriber. The baseband signal can be eitheranalog or digital in form, and is further characterized as the directelectromagnetic representation of the base information to betransmitted, with no other carrier or subcarrier energy present. Abaseband signal may be carried directly on a transmission line, such asa twisted pair of insulated copper wires or an optical fiber. A basebandsignal may also be used to modulate a carrier signal for transmission ona variety of transmission systems (e.g., radio). In telecommunications,the term “passband” describes the range of frequency spectrum which canbe passed at low transmission loss through a linear transmission system.Modulated carrier signals presented to such a system will be deliveredin their original form with minimal loss and distortion, as long as suchsignals fall within the absolute limits of the passband range offrequencies and the dynamic range of signal amplitude for a given lineartransmission system.

An example should help clarify the relationship between baseband andpassband. The electrical signal that is present at a telephone jackduring a conversation is the baseband electrical signal representationof the talker's voice. This baseband signal is typically transported tothe telephony switching office by a twisted pair of insulated copperwires. At the central office, the signal goes through the switch and istypically converted to digital form and multiplexed in the time domainfor transmission through baseband digital transmission systems thatcarry such signals on copper or fiber optic cables to other locations.The baseband digital transmission system may carry thousands ofindividual telephone calls on the same transmission line. Even thoughthere are multiple calls in progress on the same transmission line, sucha system is still defined as “baseband” because there is no modulationof a carrier or subcarrier signal anywhere in the system, and, at anygiven instant of time, there is only a single subscriber's signalactually present at a given point on the line. As the original talker'ssignal reaches the other switching office involved on the call, it isconverted back to the original analog form and put on the copper pairconnected to the far-end telephone set, once again in baseband form.

Passband techniques can also be used to provide telephony services. Incable television systems configured for telephony services, the basebandanalog telephone signal is used to modulate a carrier signal. Themodulated carrier signal can be assigned a particular frequency withinthe passband of the linear transmission system. A number of suchmodulated carrier signals, each assigned a different carrier frequencyin the passband, can be transmitted all at the same time without mutualinterference. At the far end, a selected modulated carrier signal mustbe demodulated to remove the carrier signal and recover the basebandsignal associated with the service. If the linear transmission system isoperating properly, the derived signal will be delivered to the far-endtelephone set, once again in baseband form.

While there is technology that supports digital line rates on the orderof 100 Mb/s for short-distance building twisted-pair wiring, thepractical limit for traditional twisted pair copper plant in the loopenvironment (from the serving central office to the subscriber) is onthe order of 1.5 Mb/s, at a maximum distance of about 12 kilofeet (KF).One emerging technology that is capable of attaining this practicallimit for twisted pairs is known as High-speed Digital Subscriber Line(HDSL). A similar copper-based technology known as Asymmetric DigitalSubscriber Line (ADSL) may permit the carriage of a 1.5 Mb/s downstreamsignal toward the subscriber and an upstream channel of perhaps 16kilobits per second (Kb/s), all on a single copper pair, to within 18 KFfrom the serving central office. Rather than modify its network toinclude more fiber and/or coaxial cable, at least one telephone companyis deploying ADSL technology (USA Today Apr. 29, 1993, Page B1).

While suited for their intended purpose, these emerging copper-basedtechnologies carry some uncertainties and special restrictions that mayreduce their applicability in copper loop plant. At this point, thebest-case scenario indicates that such technology could be used only onnonloaded copper loops within 12 KF (HDSL) and 18 KF (ADSL),respectively. Thus, this technology would be employable in substantiallyless than 100 percent of the present environment. Other limitations(e.g., within-sheath incompatibility with other services such as ISDN)will likely further reduce the maximum penetration percentage.

The maximum practical distance that true Broadband rates (e.g., 156 Mb/sand higher) can be supported on twisted pair copper plant is on theorder of 100 feet. Given that the emerging HDSL and ADSL copper-basedtechnologies provide line rates two orders of magnitude below truebroadband rates, and then cover substantially less than 100 percent ofthe customer base in the best case, copper is clearly not practical as atrue broadband technology solution.

Baseband signal compression techniques offer possibilities forleveraging the embedded copper plant for certain specific services.Baseband compression techniques that compress a standard movieentertainment television signal with “VCR-quality” into a 1.5 Mb/schannel (including audio) have been demonstrated, as well as lower-speeddevices intended for videoconferencing and videotelephony applications.The apparent view is that a bearer-channel technology such as ADSL(described above) and a baseband compression technology, taken together,could offer a realistic alternative for video services requiring largebandwidth, allowing continued use of the existing copper plant andobviating the need for fiber-based or other broadband links.

Unfortunately, baseband compression techniques use a deliberate tradeoffof one or more technical parameters that can reasonably be “sacrificed”as having little or no effect on a given service. For example,low-bit-rate coders for voice and video obtain bandwidth efficiencies atthe expense of transmission delay. A processing delay of perhaps ahalf-second through the encoding and decoding process will have littleor no effect on one-way broadcast service, but may disturb the naturalrhythm of speech in a two-way videotelephony application, making thetwo-way service awkward to use. Baseband compression techniques arenarrowly designed for specific applications (e.g., videotelephony)within generic classes of service (e.g., video), and do not providecomplete transparency of any baseband digital signal.

Line coding compression techniques that may be used to provide ADSLcapabilities offer bandwidth efficiencies in a variety of ways. In onecategory, Quadrature Amplitude Modulation (QAM) techniques have beenused to encode digital information for transmission on microwave radiosystems and (more recently) channel slots on cable television systems. A16-state QAM coder offers a 4 bits-per-Hertz (4 B/Hz) efficiency; a64-state QAM coder offers a 6 bits-per-Hertz (6 B/Hz) efficiency. Thissimply means that an input digital signal at the rate of 1.5 Mb/s can be16-state QAM-coded into an analog frequency spectrum of about 0.38MegaHertz (MHz), making it possible to be transported on copper wirepairs over longer distances. Similar techniques are also possible onsatellite and CATV systems, to provide both digital signal carriage anddigital spectrum efficiencies on those media.

In summary, utilizing baseband signal compression techniques results inbandwidth efficiencies which are gained at the penalty of one or moretechnical parameters. Such a tradeoff may not be possible in the case ofa different service on the same medium. In the case of wireline codingtechniques that deal with the signal after baseband compression,technical complexity and cost generally limit it to 6 B/Hz spectrumefficiency. Thus, copper-based systems such as HDSL and ADSL may findlimited application in the telephone network. HDSL is actually a purecost-saving loop alternative to facility arrangements that serve 1.5Mb/s High-Capacity digital service (“HICAP”) customers. The cost savingsare potentially realized by the ability to use assigned nonloaded pairsin the loop outside plant, rather than designed pairs, as well as goinglonger distances without outside plant repeaters.

ADSL technology could provide early market entry for limited VCR-qualityvideo or other asymmetric 1.5 Mb/s applications. Advantages of ADSLinclude the use of existing copper plant facilities and maximization ofnetwork functionality. Disadvantages include the cost of set-topconverters which are not reusable after ADSL is obsoleted. Also, ADSLoffers only single channel service. In addition, the service can onlyreach a limited number of customers and telephone service electricalnoise can result in video distortion. ADSL is also subject to RFtransmission interference over longer loops.

Fiber optic-based systems are preferable to copper-based networks evenwith HDSL or ADSL because of their high bit rate transport capability.Information services that require true broadband rates require fiber orcoaxial cable technology, as a practical matter. Even low-end (i.e.,POTS “plain old telephone service”) services will reflect a lowerper-subscriber cost on fiber, compared to present copper-based deliverysystems. Specifically, fiber-based systems that provide residencetelephony to groups of 4-8 subscribers with fiber to the curb (FTTC) areexpected to achieve cost parity with copper in the near future. However,the cost to replace the existing copper plant in the U.S. with fiberoptics is estimated at hundreds of billions of dollars. Thus the lengthof time required to achieve this conversion could be decades.

One possible alternative to fiber or copper networks is a hybrid networkwhich utilizes existing facilities and employs fiber optics, coaxialcable and copper wiring. Such a network would allow the delivery of manyadvanced services and yet be more cost efficient to allow earlierconversion to a broadband network with significant fiber opticcapability included. At least one company has announced plans for such ahybrid network (Denver Post, Apr. 24, 1993 Page C1).

In general, hybrid networks combine a telephony network and a videonetwork. One drawback of such a network is some duplication of equipmentrequired to transport the separate signals. That is, if, for example,the telephony services could be sent over the video network, then asubstantial portion of the cost and complexity of the hybrid networkcould be eliminated. However, in order to send telephony and videosignals over the same transport medium, the unique characteristics ofeach signal must be addressed. For video signals this is not asdifficult as some of the issues surrounding transport of telephonysignals. That is, video signals are generally sent in one direction,from the provider to the subscriber, while telephony requires two-waytransport. As video evolves into interactive video, however, two-wayvideo signal transport issues will also become significant.

Telephony, in addition to requiring two-way communication, has two otherrequirements not necessarily addressed by video networks: powering andprivacy of communication. In video networks the power to operate thesubscriber television set, for example, is provided by the subscriber.That is, the subscriber plugs his or her television and/or videocassette recorder into an electrical outlet which provides power in thesubscriber location. In the event of a power outage, for whateverreason, the user is unable to view the television unless he or she has abackup source of power (i.e., battery or generator). Few people havesuch backup power. In telephony, on the other hand, subscribers expectphone service whether or not electricity is available. The followingparagraphs discuss a history of power in the telephony network.

Telephones on the early manual networks had their own battery boxeswhich contained dry cells. These batteries were used to power the carbongranule microphones. In addition, a hand crank generator in the phonesupplied the needed signaling to call others on the same line, or theoperator. These two power sources within the telephone allowed a user tooriginate a call and to talk to other users. Neither of these sourceswere dependent upon household power, allowing calls to be placed evenbefore rural electrification.

When automatic switching was introduced into the network, the batterybox was replaced with a common battery located at the switch, includinga common ringing voltage source. The central office switch also neededpower to operate and make connections between users. Supplying power toeach telephone allowed current flow and the timed interruption of thatcurrent (dial pulses) to signal the switch of the user's intentions. Inaddition, the busy state current could be used by the telephone to powerthe carbon microphone.

Because of the need to protect the switch and the telephone connectionsfrom service interruptions, the power plant at the central office wasbacked up with large wet cell batteries. These batteries in turn wereoften backed up with motor-generator sets. Several different voltagesare used within the network, but the primary supply is −48 volt directcurrent (vdc) and ±105 volts at 20 Hz.

Over time as the telephone network grew in size and service penetrationapproached 100 percent, service availability (reliability) became one ofthe most important obligations of the network. For a time the telephonesin users' homes belonged to the network and were maintained by thenetwork owner. In the past 20 years the ownership of the telephone haschanged again and carbon microphones aren't used anymore. However, thenew electronic telephones with their silicon chips still rely on thenetwork to supply power for call supervision and even for memory backup.

Service availability is a responsibility shared by the network and theuser. The network is responsible for maintaining the switch andconnecting trunks as well as testing and maintaining the individuallines to each user. The user also contributes to service availability bykeeping the telephone on-hook when it is not needed, by maintainingpremises wiring and terminal equipment in good repair, and by limitingthe total quantity of equipment connected to one line.

Maintaining the batteries in the telephone's battery box was difficult.Thus network power is preferable. First of all, the financial costassociated with placing the terminal power back in the terminalequipment would be huge. The supply and maintenance of the neededbatteries would either be forgotten (like those in smoke detectors) orwould be eliminated. Both of these results would limit the user'sservice availability. The second reason that power will likely remain inthe network is due to the regulatory bodies who are concerned with“life-line” services. This relates to phone service being perceived as anecessity as pointed out above. Basic telephone service is expected tobe available to everyone at a reasonable cost 24 hours a day.

There are a few exceptions. Some services are powered by the user today.As more services are introduced in the future, the user equipmentassociated with these new services may also be non-network powered. Onegood example is Integrated Services Digital Network (ISDN) services,whether Basic or Primary Rate Interfaces. With ISDN, the network powersits portion of the circuit and the user powers the terminal equipment.Most data services also fall into this category.

Power can only be provided over a fiber optic network with greatdifficulty and expense. As discussed above, power can and is easilyprovided over a copper-based network. There are video systems todaywhich utilize cable phone systems in which telephony is provided over avideo network system. However, such systems require power supplied bythe subscriber, usually in the form of AC power and (in some cases)batteries at the subscriber premises. In addition, adaptive hardware inthe form of converter boxes are needed to utilize the phone system.

Safeguarding privacy of communications is a fundamental rule in thetelephone industry. This is required by law and violators are subject toheavy penalties. Telephone subscribers have the expectation that theirusage and their communications will be kept confidential. Therequirement for privacy extends to the identity of the parties to thecommunications, and even to the fact that the communications took place.Traditional loop plant architecture provides each subscriber a dedicatedtransmission path all the way back to the switching central office.Except for the deliberate case of multiparty service, the physical“star” topology ensures that every subscriber's communication is notavailable to others who are not a party to the communications. Referringto FIG. 1, a star type network architecture is shown. A stararchitecture is a physical point-to-multipoint arrangement. There aretwo types of star architectures. In FIG. 1A a private line type of staris shown. That is each of lines 1, 2, 3, . . . (n) is separate anddistinct and provides a dedicated transmission path to the centraloffice. In FIG. 1B a party line type of star is shown. In this case eachof the parties commonly connected in this manner may listen to any ofthe others. There is no privacy. Such party line configurations, oncecommon for cost reasons, are gradually being eliminated as networks aremodernized.

Cable television systems are configured in a broadcast bus architecture,and all services carried on such systems are inherently available to allsubscribers connected to the bus, including telephone channels carriedin the passband. A logical bus type of architecture is illustrated inFIG. 2A. In a bus architecture all users share common bandwidth as in aparty line star architecture. Generally, cable companies employ a“tree-and-branch” style bus architecture (FIG. 2B). This is essentiallya logical bus on a tree and branch physical structure. Similarly, aparty line architecture (FIG. 1B) is essentially a logical bus on aphysical star. In any event, the bus style architecture used by cablecompanies, while sufficient for delivery of video services, does notensure privacy of communications for telephony or interactive videoservices. While encryption techniques can be used to mitigate thepotential problem, they add cost and are not foolproof. As interactiveservices that use voice-response units flourish, more mass-marketcustomers will routinely be touchtoning such information as credit cardnumbers and PIN authorizations. Any bus-based architecture that providestelephony or interactive video services capability must incorporatemeans to ensure privacy of communications.

Finally, it is necessary to provide some means to segregate services(commonly termed “grooming” in the telephone industry) provided by thecentral office into two basic categories: “switched services” (e.g.POTS) that terminate on the line side of the central office switchingmachine; and “special services” (e.g. burglar alarm, program channelservices, etc.) that terminate on other equipment in the central office.The segregation into these two categories is accomplished in moderntelephone networks by the use of equipment that provides for Time SlotInterchange (TSI) of digital signals.

Modern digital switches recognize only signals which are transmitted indiscrete digital rate and format. That is, the switch views thetransmitted/received signal in 64 Kb/s increments. In order to make thesignal intelligible to the switch, it must be presented in this basicformat. For POTS, the switch expects to “see” a digital signal with aspecific line code, line rate, ones density, frame format, and signalingbit convention, with other bits used for mu-law voice coding of thetalker's voice. Special services signals are not usually in a formrecognizable by the switch. Conventional networks use pulse codemodulation techniques to convert from analog to digital and vice versaand then use time division multiplexing to order to sequence (package) anumber of services in a common bit stream for transmission. Timedivision multiplexing divides the time during which each message istransmitted along the data link into discrete time intervals. Each porton the multiplexer is then sequentially sampled for the time intervaland that data sample is transmitted sequentially or serially with anumber of other data samples from other ports. A demultiplexer at thereceiving end of the transmission then recombines the seriallytransmitted data into the port corresponding to the signal origin. Whilesuited for its intended purpose, this type of transmission techniquerequires expensive time slot interchangers to reorder the time slots toseparate switched services from special services. In addition, the TSItechnique is not transparent to all of the bits. That is, the ability toperform certain functions such as cyclic redundancy check code (CRC6) onan end-to-end basis is lost with the TSI technique.

SUMMARY OF THE INVENTION

The invention is a network for providing video and telephony services toa subscriber. The network incorporates fiber optic cable, coaxial cable,and twisted pair copper wiring. The network provides power for thetelephony services from a network location through coaxial and copperwiring to the subscriber. Power can be provided over coaxial cablerelatively easily. Thus, in the hybrid network power for the telephonyportion of the service is provided through the network from the point atwhich coaxial cable and copper are used. Interdiction devices are usedto selectively transmit video signals to a subscriber location.

The invention relies on the use of fiber/coax passband infrastructure asthe basic bearer channel for all services in the residential mass marketserved by the network. The selective delivering device would bephysically located in place of a curbside Optical Network Unit (ONU),and subsumes all of the basic telephony functions (“talk” battery,ringing, testing, etc.). The selective delivery device operates as thesource/sink element for baseband telephony, is powered over the coaxialcable plant from the optical node typically serving up to 400subscribers, and provides complete transparency for the entire two-waypassband spectrum into 4-8 homes, except for the channel slots used totransport telephony services. In one embodiment the actual link to thehome consists of a twin-coaxial-cable “drop” that derives the tip/ringRJ-11 interface from the center conductors of the coaxial cable pair ata Network Interface (NI), compatible with all existing inside telephonywire arrangements. The other output of the NI is a standard F-fittingCATV connector, compatible with the existing coaxial cable inside wire.The curbside device also houses the passband interdiction device. In thepreferred embodiment, the NI at the residence includes only passivefilters and no active electronics.

The invention addresses the issue of communications privacy bypermanently interdicting all of the telephony channels in the passbandfor both directions of transmission. The interdiction is accomplishedexternal to the premises of all subscribers so served. No modulatedtelephony signal ever appears in recoverable form on the coaxial cabledrop, ensuring complete privacy of communications. This interdiction canbe accomplished by several means. One method involves the permanentinsertion of a truly random jamming signal in the part of the passbandthat contains the telephony passband channels in the direction oftransmission toward the customer. An alternative method involves the useof a negative trap (e.g. band-stop filters) that prevents any of thetelephony passband channels from reaching the drop cable toward thesubscriber. In the set of passband frequencies for the upstreamdirection of transmission (toward the central office), an isolationamplifier and suitable directional coupler arrangement prevents anyindividual subscriber from monitoring the upstream telephony channels ofother telephony subscribers on the bus. Conventional jamming or negativetrap techniques in the upstream direction of transmission are notappropriate, since there are other applications that originate from thesubscriber premises that use a portion of the upstream frequencies. Thisrequires transmission transparency from the subscriber toward thenetwork. A preferred embodiment of the invention uses a modifiedinterdiction device external to subscribers' premises to accomplish thisfunction.

Nonswitched telephony special services (burglar alarms, etc.) must besorted from ordinary switched telephony services. In the preferredembodiment, the present invention performs this function by frequencyassignment at the remote telephony channel modulators and demodulators.This is accomplished by remotely setting both transmit and receivefrequencies of the individual channels from the central office. At thecentral office, the blocks of switched services of modulated telephonychannels in the passband are converted to/from the framed digital formatrequired by the telephone switch, and the blocks of nonswitched specialservices are converted to the framed digital format and bypass theswitch, or are further transported to other locations. Thus, use of theTime Slot Interchange (TSI) technique with its assorted limitations andhigh cost equipment is eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a “star” type network architecture with a privateline architecture (FIG. 1A) and a party line architecture (FIG. 1B);

FIG. 2 illustrates a “bus” type architecture with a traditional bus(FIG. 2A) and a cable type bus (FIG. 2B);

FIG. 3 illustrates a broadband hybrid fiber/coaxial cable networkarchitecture;

FIG. 4 illustrates an alternate hybrid fiber/coaxial cable networkarchitecture;

FIG. 5 illustrates a preferred embodiment of the invention for a hybridfiber/coaxial cable network architecture;

FIG. 6 is a schematic illustrating a baseband below passband curb unit;

FIG. 7 is a schematic illustrating the interdiction device to ensureprivacy protection for the preferred embodiment;

FIG. 8 is a schematic illustrating a network interface for the preferredembodiment; and

FIG. 9 is a more detailed drawing illustrating the combiner and splitterunit; and

FIG. 10 illustrates network line cards.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Like reference numerals will denote like structure throughout thedescription of the various figures. Referring to FIG. 3, a broadbandhybrid fiber/coaxial cable network architecture is shown. A digitalswitch 11 and a video transmission device 12 including RF modulators 9and electric/optical converters 10 are shown in a central office 13.Digital telephony signals are carried over DS1 lines 6 through SONETmultiplexer 19 to a fiber optic cable 14. This architecture represents afiber to the curb (FTTC) type of architecture with a video remotetransport overlay. That is, fiber optic cables 14 carry digitaltelephony signals (SONET OC3) from the central office through a remotedigital terminal 18 to an optical network unit 15 (ONU). ONU 15 mayinclude a video interdiction device 16 or interdiction device 16 couldbe separately located as shown in FIG. 3. The analog video signals(AM-FDM) from a number of video information providers 23 are carriedthrough fiber optic cable 14 to one or more remote nodes which mayinclude an analog passband video receiver 17 which includesoptical/electrical converters where the analog optic signals areconverted to analog electrical signals on a coaxial cable 24.

A power supply cable 20 which may be a 22 gauge electrical cablesupplies power directly from power source 32 in central office 13 tooptical network unit 15. From optical network unit 15 telephony servicesmay be provided to subscriber premises 21 over a conventional twistedcopper pair line 22 to a telephone 27. Typically an ONU serves up toeight subscriber locations. Video services from a number of videoinformation providers 23, such as satellite systems or videostorage/retrieval equipment, or other suppliers are provided tosubscriber premises 21 through coaxial cable 24. A video set-topconverter 25 may or may not be required to descramble these videosignals to a television 26.

The network depicted in FIG. 3 avoids several problems associated withthe delivery of telephony and video signals to the home. That is, sincethe signals are carried on separate transport systems, each of thesignals may be treated separately. For example, telephone 27 insubscriber premises 21 may be powered from central office 13 as is donein conventional telephony. Powering of the set-top converter 25 andtelevision 26 may be done from subscriber premises 21. In addition,privacy issues with respect to telephony services over copper wire 22are maintained as in a conventional telephony network. As is known inthe art, more than one ONU could be connected to terminal 18. Similarly,more than one interdiction tap 16 could be connected to receiver 17. Thedrawbacks with the network shown in FIG. 3 include complexity and cost.That is, fiber optic cable 14, power cable 20, and coaxial cable 24 mustbe laid from each central office 13 to each optical network unit 15 orsubscriber premises 21. In addition, additional equipment such as remotedigital terminals 18 are required to efficiently transport the opticalsignals.

Referring to FIG. 4, an alternate hybrid fiber coax network isillustrated. As with FIG. 3, central office 13 includes telephone switch11 and video transmission equipment 12 from which a system manager 28controls various ancillary functions of video services supplied fromproviders 23. As with the architecture in FIG. 3, telephony signals andvideo signals are carried from central office 13 on fiber optic cable 14through the feeder portion of the outside plant 29. The telephonysignals are passed through remote digital terminals 18 and suppliedthrough fiber optic cable 14 to optical network unit 15. The videosignals are transported to video receiver 17 where they are convertedfrom optical to electrical signals on coaxial cable 24. The videosignals are then supplied to interdiction device 16 at the location ofthe optical network unit 15. In this embodiment ONU 15 and interdictiondevice 16 are connected and preferably co-located. The major differencebetween FIG. 4 and FIG. 3 is that power may be supplied through coaxialcable 24 by a power supply 32 which may include an electrical connectionto the electrical utility and backup batteries. Thus, power supply cable20 in FIG. 3 is eliminated.

The elimination of power supply cable 20 represents a significant costsavings over the architecture of FIG. 3. As with FIG. 3, the videosignals through coaxial cable 24 are supplied to customer premises 21through interdiction unit 16 contained in optical network unit 15. Poweris now supplied to telephone 27 from power supply 32 through coaxialcable 24 and ONU 15. Coaxial cable 24 from interdiction device 16 tocustomer premises 21 supplies only video signals to television 26 anddoes not supply power. As with FIG. 3, a video set-top converter 25 mayor may not be included in the system. FIG. 4 represents a substantialimprovement over the network shown in FIG. 3 in that the elimination ofpower supply cable 20 results in significant cost savings and simplifiesthe architecture.

While the architecture of FIG. 4 is an improvement on that of FIG. 3, itwould be even more significant if the telephony signals and the videosignals could be carried on a common transport system, thus eliminatingthe duplication of fiber optic cables shown in both FIG. 3 and FIG. 4.By carrying the video and telephony signals over a common integralnetwork transmission system, however, other issues are raised. Chiefamong these issues is a privacy issue. That is, if the telephony andvideo signals were both sent to the subscriber premises 21 over the sameline, it may be possible for a subscriber to “tap” into the telephonysignals of all neighbors connected to the coaxial cable bus. This wouldbe done by tuning and demodulating from the myriad of carrier channelson the coaxial cable in the telephony signal range. It would berelatively easy for one minimally skilled in electronics to devise meanswhich could “tune in” on these telephony channels carried in thespectrum. This is possible because the other telephony signals in theexample would also emanate from the remote optical node 17. With onecoaxial cable system carrying all of these signals a subscriber is ableto access the signals of these other subscribers.

Referring to FIG. 5, the preferred embodiment of a fiber/coax transportarchitecture is shown in which the telephony and video signals aretransported through a common integral network. That is, central office13 includes telephony switch 11 and video transmission equipment 12 asshown in FIGS. 3 and 4. Alternative video suppliers 23 could supplyvideo signals to video transmission equipment 12. Telephony signals fromswitch 11 and from special services equipment 33 are supplied to adigital conversion RF modulator/demodulator unit 34. The telephonysignals must be modulated to be transported on the analog passband fiberoptic cable 14. The video signals from video transmission equipment 12are combined with the telephony signals in a combiner transceiver unit35. These optical signals are sent (and received) on fiber optic cable14 to/from an optical node 17 which includes an optical/electricalconversion unit as shown in FIGS. 3 and 4. The remote digital terminal18 as shown in FIG. 4 is eliminated because the distribution function itperforms is no longer needed. Power plant 32 is co-located with opticalnode 17. By elimination of remote digital terminal 18 and the associatedfibers in the main fiber optic cable, significant cost savings areachieved by this architecture over that shown in FIG. 4. It is theelimination of remote digital terminal 18 on the ONU 15 which raises theprivacy issue. The combined telephony and video signals from opticalnode 17 along with the power supply from power plant 32 are carried oncoaxial cable 24 to a selective delivery means which may include aBaseband Below Passband (BBP) device 37. Device 37 includes many of thefunctions performed by optical network unit 15 in FIGS. 3 and 4 withsignificant additions and modifications. Telephony and video signals aresupplied to telephone 27 and television 26 on subscriber premises 21through a network interface 43.

Referring to FIG. 7, BBP unit 37 is shown in greater detail. BBP device37 includes an interdiction device 16 also used for telephony, amodulator/demodulator unit 39, and a power converter unit 41.Interdiction device 16 is a modification of the standard interdictiondevice known in the art and used in video networks. That is, a devicesuch as an eight-port interdiction unit available from ScientificAtlanta Corporation (Model No. 9508-021) may be so modified. Thestandard interdiction device uses a jamming oscillator 49 to jam certainchannels and transmit only those which are made available to thesubscriber. Alternatively, a negative trap (consisting of band-stopfilters) could be used in place of oscillator 49 as an interdictiondevice to attenuate the nondelivered channels below the noise floor.Interdiction device 16 is modified in the preferred embodiment byincluding isolation amplifiers 47 and forward coupler 48 in the upstreamdirection of transmission such that only the baseband telephony signalto and from the subscriber to be served is available at a givensubscriber location. That is, the standard interdiction device ismodified so that all of the downstream telephony channels areinterdicted and each upstream 5-30 MHz port is isolated. Thus, asubscriber is prevented from tuning into telephone calls of othersubscribers on the network.

Referring to FIGS. 5, 6, and 7, the privacy protection afforded by thepresent invention is illustrated. Central office 13 sends video andtelephony signals “downstream” to subscriber's premises 21 and receivessignals associated with video as well as telephony signals sent upstreamfrom subscriber's premises 21. The architecture is essentially a “bus”type architecture (see FIG. 2). Thus, absent any precautions, eachsubscriber could monitor the video and/or telephony signals from othersubscribers on the bus. For downstream video this is not a problem. Thecable television company today uses this type of system and the onlyconcern is to interdict (jam or trap) selected premium channels whichthe subscriber has not paid for. However, if interactive video and/ortelephony are added, privacy becomes important.

In order to ensure privacy in this type of network, in addition tointerdiction device 16 and modulator/demodulator device 39, additionalprotection is needed. Unless modified, interdiction device 16 ensuresthat only selected downstream video channels are delivered to subscriberpremises 21. Modulator/demodulator device 39 ensures that only selectedtelephony channels are delivered to and from subscriber premises overthe telephone line. However, for interactive video and to prevent theselective tuning to other subscribers telephone channels through theinteractive video line 24 connected to F-fitting connector 46,additional interdiction is needed. In the preferred embodiment,isolation amplifier 47 and forward coupler 48 are added to a modifiedjamming oscillator 49 in interdiction device 16.

Amplifier 47 and coupler 48 may optionally be combined with bandpassfilters (not shown) as is known in the art to selectively transmit asubset of upstream signals. As discussed above the 5-30 MHz bandwidth isused for telephone and interactive signals associated with videocommunications. There are three usable 6 MHz channels in this bandwidthfrom approximately 8-26 MHz. Since each 6 MHz channel can carry over 400individual telephony channels, only two channels would generally beneeded for telephony in the preferred embodiment. The other 6 MHzchannel is available for interactive control/request signals associatedwith video services. Amp 47 and coupler 48 (optionally with selectivefilters) selectively transmit only the interactive signals associatedwith video channels in the upstream direction. All of the channels usedfor telephony are eliminated in the downstream direction by interdictiondevice 16. Thus, there is no way for any particular subscriber to listento the telephony channels of another subscriber in either direction oftransmission. Privacy is thus assured.

Referring to FIGS. 5 and 6, modulator/demodulator device 39, which maybe a cable telephony device such as “CablePhone®” which is commerciallyavailable from Jerrold, Inc., demodulates the telephony signal fromcoaxial cable 24 and may send the demodulated telephony signal throughstandard copper tip and ring wires 42 directly to telephone 27.Modulator/demodulator unit 39 also receives the baseband telephonysignals from telephone 27 in subscriber premises 21 and modulates thatsignal onto coaxial cable 24. Optionally, modulator/demodulator unit 39could send the baseband telephony signal to combiner 44 to be combinedwith passband signals such as video onto coaxial cable 24. BBP device 37also includes a power converter 41 which supplies −48 volt DC power,±105 volt AC ringing power, and other converted power for themodulator/demodulator unit 39 to power the telephone 27 as in a standardtelephony network.

Referring to FIGS. 5, 6 and 7, telephone 27 and television 26 onsubscriber premises 21 receive the video and telephony signals through anetwork interface 43. In the embodiment shown in FIG. 5, the videosignals from interdiction device 16 and the telephony signals frommodulator/demodulator device 39 are combined in a combiner unit 44 (FIG.6) and then sent over dual coaxial cable drops to a splitter. Referringto FIG. 8, splitter 36, 38 is contained in the network interface unit43. That is, passive electronics are also included in network interface43. The network interface unit 43 includes a high pass filter 36 with DCblocking to provide RF transparency for all passband frequencies and toblock all telephony signals. A low pass filter 38 with DC transparencyremoves RF passband energy and passes all telephony signals. A twincarbon block protector unit 50 is also included as is known in the art.A standard RJ-11 telephony connector 45, and an F-fitting connector 46which is standard in the video cable TV network are included. Becausethe connectors 45 and 46 are standard, the subscriber premises would nothave to be rewired or locally powered to deliver services from thisnetwork. While the embodiment shown is the preferred embodiment, it isalso possible to connect the coaxial cable from modified interdictiondevice 16 directly to the network interface F-fitting 46 and the copperwire 42 from modulator/demodulator device 39 directly to the RJ-11connector on network interface 43. In either event, the modulatedtelephony signals which would otherwise be carried onto coaxial cable 24along with the video signals are eliminated at interdiction device 16such that only the demodulated telephony signal from demodulator device39 is available to a particular subscriber. Thus, any possibility of asubscriber eavesdropping on telephone calls from other subscribers iseliminated. If more than one coaxial cable bearing video services issupplied to network interface 43, a P-Intrinsic-Negative (PIN) diodeswitch or other devices known in the art, for example, could be used toallow the subscriber to select which set of services he or she wouldprefer at any particular time.

The BBP unit 37 enables the network architecture shown in FIG. 5 toprovide the best features of the two basic wire line approaches toresidential access architecture (baseband FTTC and passband cabletelevision) and solves for the respective problems of each approach at acost significantly less than utilizing both types of network as shown inFIGS. 3 and 4. The network architecture disclosed in FIG. 5 provides atrue broadband network that subsumes all existing services and allfuture services for telephony and video services at a cost substantiallyless than other types of hybrid networks.

Referring to FIG. 9, a more detailed description of the combiner 44 andsplitter 36, 38 is shown. As previously described, combiner 44 iscontained in BBP unit 37. Combiner 44 preferably includes commerciallyavailable L-Section filters 52 shown schematically. These filters arecontained in RF-shielded enclosures 53 providing greater than 65 dB ofisolation between each of coaxial cables 24 over the passband. Thesplitter includes commercially available high pass filters 36 andlow-pass filters 38 contained in network interface 43. As with thecombiner, the filters are contained in RF-shielded enclosures 53providing more than 65 dB of isolation between coax cables 24 which areconnected to F-fitting 46.

The present invention uses frequency division rather than Time SlotInterchange (TSI) techniques to map the signals for transmission. By sodoing, the cost associated with TSI equipment and the nonenablement ofcertain functions such as monitoring signal degradation (CRC6) isremoved. Although TSI could be employed in the network of the presentinvention, frequency assignment techniques are preferred because thesignals are already in the frequency domain for transmission. Thepresent invention uses a linear channel which simultaneously transmitsthe signals parallel in time rather than in series in time. There is nomutual interference among the simultaneously transmitted signals in thelinear channel because they are transmitted at different frequencies.

Referring to FIG. 10, frequency division signal transmission isaccomplished by remotely setting the specific transmit and receivefrequency pairs for each channel card 51 in BBP device 37. Thus,segregation of switched services and special services into respectiveportions of contiguous spectrum is accomplished at the location nearestthe user of the services. At central office 13 the RF modulated channelsare converted to/from 64 kilobit per second (64 Kb/s) channels that aregrouped together in blocks of 24, then formatted into a standard framedDS1 signal for termination on the digital switch 11. DS1 signalscomposed of only special services are routed to other terminalequipment, or transmission equipment for carriage to other locations.This approach allows the bulk conversion of groups of modulated carriersignals to/from DS1 digital signals, obviating the need for either TimeSlot Interchange or individual carrier frequency translation ahead ofbulk A/D conversion at central office 13. Another advantage of theapproach is having “universal” channel cards 51 within a given type ofservice that can be installed in any slot in any BBP device 37. Thus,spare/replacement inventories of each are kept to a minimum. Thefrequency pairs associated with each card are set and controlledremotely, preferably in central office 13, such that the users may notalter the cards.

Each subscriber is assigned a unique transmit and receive frequency pairfor telephony and special services. The assigned frequency pair iscontrolled from central office 13. Thus contiguous frequency assignmentto card 51 in BBP device 37 is achieved. This permits grouping ofnonswitched special services that will not terminate on the digitalswitch. Time slot interchange segregation of special and telephonyservices at central office 13 is eliminated. Since an optical node 19could serve as many as 50 BBP curb devices 37, the frequency divisiontechnique allows for assignment of any available frequency pair to anyservice channel card 51 at the BBP device 37, regardless of physicallocation of the BBP device 37.

There are several significant benefits of the new BBP element. The firstis the elimination of the baseband fiber-to-the-curb (FTTC) portion ofpreviously known hybrid networks. This is made possible by theincorporation of the telephony services in the passband portion of thenetwork, greatly simplifying the overall complexity of the outside plantportion of the architecture. The telephony services are provided by acable telephony method which employs signal modulation with someimportant differences. Since talk battery and ringing voltage arepowered from the network, local (inside home) powering problems areeliminated. Since the passband frequencies that carry telephony servicesare blocked beyond the selective delivery device, it is not possible tomonitor other telephone subscribers' communications from a givenresidence. Thus, the privacy issues associated with telephony servicespreviously provided through hybrid video-type networks are eliminated.

While the invention has been disclosed with respect to a preferredembodiment, changes and modifications may be made which are within theintended scope of the invention as defined by the appended claims.

FIG. 1A illustrates a private line “star” type network architecture;

FIG. 1B illustrates a private line “star” type network architecture;

FIG. 2A illustrates a traditional “bus” type architecture;

FIG. 2B illustrates a cable “bus” type architecture;

1. A system for providing selected two-way special services to asubscriber location comprising: a logical bus network including acoaxial cable network having at least a first signal path and a secondsignal path to and from said subscriber location for transportingmodulated carrier signals in a downstream and upstream frequency rangeto said subscriber location; and a selective delivering deviceelectromagnetically connected to said logical bus network, saidselective delivering device interdicting modulated carrier signals insaid downstream frequency range on said second signal path and isolatingmodulated carrier signals in said upstream frequency range on said firstand second paths, said selective delivering device demodulating selectedmodulated carrier signals in the downstream frequency range on saidfirst signal path and modulating carrier signals in the upstreamfrequency range on said first signal path wherein said carrier signalsto and from said subscriber location cannot be monitored at anothersubscriber location on said logical bus network.
 2. A system accordingto claim 1 wherein said selective delivering device includes: aninterdiction device operatively associated with said network to allowonly preselected frequency signals to be transmitted upstream ordownstream on said network; and a modulator/demodulator operativelyassociated with said coaxial cable network to deliver one or moreselected two-way special services to a subscriber location.
 3. A systemaccording to claim 1 further including means, operatively associatedwith said coaxial cable network, for supplying power to a subscribertelephone through said coaxial cable network.
 4. A system for providingvideo and telephony services to a subscriber comprising: means forproviding modulated telephony signals to and from a combined networktransmission system, said combined network transmission system includinga fiber optic transmission system and a network coaxial cable system;means, operatively associated with said combined network transmissionsystem, for supplying video signals on said combined networktransmission system; means, operatively associated with said fiber optictransmission system, for converting said telephony and video opticalsignals on said fiber optic transmission system to telephony electricalsignals and video electrical signals on said network coaxial cablesystem, and for simultaneously converting said video and said telephonyelectrical signals on said network coaxial cable system to video andtelephony optical signals on said fiber optic transmission system;means, operatively associated with said combined network transmissionsystem, for selectively delivering said video signals; means,operatively associated with said network coaxial cable system, forproviding demodulated telephony signals; means, operatively associatedwith said selectively delivering means and said providing means, forcombining said selectively delivered video signal and said demodulatedtelephony signals onto a coaxial cable system of said subscriber; andmeans, operatively associated with said subscriber coaxial system forseparating said demodulated telephony signals from said selectivelydelivered video signals.
 5. A system according to claim 4 furtherincluding: means, operatively associated with said network coaxial cablesystem, for furnishing power; and means, operatively associated withsaid network coaxial cable system, for transforming said power.
 6. Asystem for delivering video and telephony services to a subscribercomprising: a transport network including a fiber optic system and acoaxial cable system; means, associated with said transport network, formodulating/demodulating a baseband telephony signal; means, associatedwith said fiber optic system, for supplying a video signal on said fiberoptic system; an optical/electrical signal converter connected to saidfiber optic system and said coaxial cable system; an interdictiondevice, connected to said coaxial cable system; a modulator/demodulatorconnected to said coaxial cable system; means, connected to saidinterdiction device and said modulator/demodulator device, for combininga noninterdicted video signal and said baseband telephony signal; andmeans, connected to said combining means, for separating saidnoninterdicted video signal from said baseband telephony signal.
 7. Avideo and telephony network including a plurality of telephonesoperatively connected thereto comprising: a fiber optic transmissionsystem; a coaxial cable transmission system connected to said fiberoptic transmission system; a telephone switching system associated withsaid fiber optic transmission system; a video provisioning systemassociated with said fiber optic transmission system; an interdictionunit operatively associated with said coaxial cable system; and amodulator/demodulator operatively associated with said coaxial cablesystem; whereby telephony signals and video signals on said coaxialcable system are interdicted such that only selected telephony signalsare transmitted to and from said telephones.
 8. A network according toclaim 7 further including: means, operatively associated with saidcoaxial cable system, for combining an interdicted video signal and ademodulated telephony signal on a subscriber coaxial cable system; andmeans, operatively associated with said subscriber coaxial cable system,for separating said interdicted video signal from said demodulatedtelephony signal.
 9. A network according to claim 7 further includingmeans, operatively associated with said coaxial cable system, forsupplying power to said telephones.
 10. A telephony network comprising:a central office including a digital switch and a special serviceequipment; a transport system operatively connected to said switch, saidtransport system including a fiber optic system and a coaxial cablesystem connected to said fiber optic system; a plurality of line cardsoperatively associated with said coaxial cable system; each said linecard including a preselected frequency pair assigned thereto, saidpreselected frequency pair corresponding exclusively to either atelephony service or a special service; means, associated with saiddigital transport system, for recognizing said assigned frequency pair;and whereby a signal from said line card is routed to said digitalswitch if said assigned frequency pair is recognized as a telephonyservice and a signal for said line card is routed to said specialservice equipment if said assigned frequency pair is recognized as aspecial service.
 11. A network according to claim 10 wherein said linecard is included in a BBP device adjacent to a subscriber location. 12.A network according to claim 10 further including means, associated withsaid transport system, for remotely assigning said frequency pair. 13.An apparatus for delivering video and baseband telephony signals to asubscriber on a coaxial cable network comprising: a network interface; abaseband below passband unit connected to said network interface; asignal combiner operatively associated with said baseband below passbandunit, said combiner including at least one pair of L-filters to allowbaseband telephony signals to be added to passband video signals; and asignal splitter connected to said coaxial cable network, said splitterincluding a high pass filter and a low pass filter such that said highpass filter permits transmission of all passband signals and blocks alltelephony signals, and said low pass filter blocks all passband signalsand permits transmission of all telephony signals.
 14. A device forselective delivery of telephony signals in a coaxial cable network suchthat said telephony signals from a particular subscriber can not bemonitored by another subscriber on said network said device comprising:an interdiction device connected to said coaxial cable network to jamselected video signals and all telephony signals, said interdictiondevice including: a jamming oscillator connected to said coaxial cablenetwork; an amplifier connected to said coaxial cable network; a forwardcoupler connected to said coaxial cable network; and amodulator/demodulator connected to said coaxial cable network to deriveselected baseband telephony signals for said particular subscriber. 15.A device for selective delivery of telephony signals in a coaxial cablenetwork comprising: an interdiction device connected to said coaxialcable network, said interdiction device including: a negative trapconnected to said coaxial cable network; an amplifier effectivelyconnected to said coaxial cable network; a forward coupler connected tosaid coaxial cable network; and a modulator/demodulator connected tosaid coaxial cable network; whereby said interdiction device eliminatesall telephony signals and said modulator/demodulator device derivesselected baseband telephony signals for a particular subscriber suchthat said baseband telephony signals for said particular subscriber cannot be monitored by a different subscriber on said network.